He is free to go wherever he wants until he is charged. It's just that if he goes outside the Ecuadorian embassy, he will be charged.
Why can't he be charged while he's still in the Embassy?
I understand that enforcing any judgement rendered by a court becomes a hang up because of his asylum, but that's a separate concern.
I'm really sad that his hasn't gone to the European Court of Human Right to decide against Sweden (or England, because it is actually England that is keeping him locked up).
Note that I do not have a high opinion of Assange, and it is quite possible that according to Swedish law he did rape those women. But he should have been entitled to a trial in absentia.
So he only has another 4 years to go